The present invention relates to rotary bore hole apparatus, and more particularly to replaceable working tools and devices used with drill strings or tubular products for special purposes.
It is often required in drilling operations to use a member or device for a temporary purpose at some point or region along the drill string. For example, a stabilizer is a device which is mounted on a drill string section or collar to control lateral deflection of the drill string in that region and prevent the drill string from contacting the sides of the well bore hole. The stabilizer comprises a device of larger diameter, usually having curved blades that have hardened outer faces, that can maintain the drill string concentric even though the bore hole is curved. Most such stabilizers are attachable in-line, as another element in the drill string, and therefore must be threaded into the string in series with pipe and collar elements. There are many problems encountered in the use of these devices, including thread or shoulder seal damage during improper makeup. The use of added tool joints in the string increases the number of points at which twist-off and wash-out failures can occur, and increases the chances of loss or sticking of the stabilizer in the bore hole. Such devices cannot be mounted at freely chosen positions along the drill collars, and are usually large, heavy and expensive. Further, installation and removal of such stabilizers must be done on the rig floor, entailing corresponding high expenses for equipment and crew.
Releasable or removable drill string stabilizers have therefore been devised that can be mounted at selected locations along the length of a drill collar, by various disengageable mechanical means. Threaded, clamping, wedging and other arrangements have been employed for holding the stabilizer in position during use and subsequently permitting removal. All are essentially friction-locking devices, as exemplified by U.S. Pat. Nos. 4,245,709, 4,258,804 and 4,275,935. These devices are however subject to numerous problems when used in practical situations. For example, when used in directional (i.e. curved or angled) holes, the bending and torsion forces exerted on a friction device tend to cause it to lose its grip or fail, depending upon the amount of torque exerted during make-up. Devices which slip can ride down the drill string and be collected on the top of the bit. Moreover, if a friction-locking device is attached to a worn drill collar, there is often insufficient gripping surface because collars can have an egg shape or out of round distortion. When the friction members are damaged or worn during use, extended down time is often required to remove them from the drill collar. Releasable stabilizers as heretofore employed are also expensive devices having limited useful life.
The stabilizer is merely one example of a device or tool that can advantageously be removably attached to a drill string. Roller reamers and midcollar hardbands are other examples of devices that have a larger outer diameter than a drill string section on which they are mounted. The former are commonly used for bore hole sizing and the latter are used in counteracting excessive wear that sometimes arises with abrasive formations. Also down-hole stabilizers and other devices are sometimes used with heavyweight tubular sections that are employed in high load bearing regions of a drill string and present different operative problems. It is desirable that removable tools be usable in this context as well.
It should be recognized that stabilizers and other down-hole devices that engage bore hole walls can be subjected to extremely high circumferential forces that accentuate the mechanical problems. In addition, high linear forces can be encountered when running in or pulling out of tight holes or damaged casing. An ability to withstand these forces without slippage or disengagement is a primary requirement for field use.
The present invention provides economic releasably attachable drill string devices adapted to be mounted on a drill string member, without using friction-type elements or components for engagement or disengagement.